Mesoporous nanostructures of Nb2O5 obtained by an EISA route for the treatment of malachite green dye-contaminated aqueous solution under UV and visible light irradiation

Abstract A series of mesoporous Nb2O5 photocatalysts was synthesized via an evaporation-induced self-assembly (EISA) method using NbCl5 and Pluronic P123 as precursor and templating agent, respectively. The obtained samples are subsequently calcined at 380, 480 and 580 °C and are assigned as mNb2O5-380, mNb2O5-480 and mNb2O5-580, respectively. For comparison, niobia samples were also prepared by a simple hydrolysis method and condensation of niobium chloride in the absence of templating agents assigned as bulk sample. All materials were characterized by XRD, FE-SEM, UV–vis DRS, FTIR, TG/DTA and BET techniques. It is exciting that the absorption edge of the EISA samples calcined at higher temperatures shifts several nanometers to the visible region compared with hydrolysis synthesized and commercial samples in the UV–vis absorption spectra, indicating their absorbance extended in the visible region. The photocatalytic decolorization of malachite green (MG) over the photocatalysts under UV and visible light sources was also investigated. We found the photocatalytic activity of mNb2O5-380 with about 140 m2 g−1 surface area was higher than that of the commercial Nb2O5 and TiO2 P25 photocatalysts and synthesized bulk sample for MG decolorization under visible light irradiation, whereas TiO2 P25 showed higher photocatalytic activity under UV irradiation. The decolorization kinetics of MG was followed by a first-order reaction with an apparent rate constant of k=1.0×10−2 min−1 for the mNb2O5-380 photocatalyst, the sample with the highest activity among all as-prepared samples under visible radiation. Meanwhile, the maximum decolorization of MG under visible light was obtained at 0.5 g L−1, 5 mg L−1 and 8.2 as optimum values for the dosage of mNb2O5-380 photocatalyst, dye concentration and pH, respectively.